sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是

Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 cos(a+B)×cos(a-B)=1/3,求cos^2(a)-sin^2(B)的值 若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a 若cos(a+b)·cos(a-b)=1/3,则cos^2 a-sin^2 b的值是? 已知4sin asin b=根号2,4cos a cos b=根号6,则cos 2a+cos 2b的值是? 已知sin[a-b]cos a-cos[b-a]sin a=3/5,b是第三象限角,求sin[b+5π/4]的值 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明 1.若sin a+sin b=ㄏ2/2,则cos a+cos b的取值范围是多少? cos^B-cos^C=sin^A,三角形的形状 解三角函数已知 sin(b)+cos(b)=a 求a的值sin(b)*cos(b)=a 若a,b属于(0,90°),sin(a-b/2)=3/5,sin(a/2-b)=-1/2,则cos(a+b)/2的值